Laird, Edward Dylan (2016-08). Characterization of Antibiotic Resistance Profiles of Surface Water Bacteria in an Urbanizing Watershed. Master's Thesis.
Wastewater treatment plants (WWTP) are typically incapable of addressing the influx of antibiotics (AB), and may act as a harbor for the selection and proliferation of antibiotic resistant bacteria (ARB). In order to examine the influence of WWTP discharge on the AB resistance profiles of surface water bacteria in an urban stream setting, E. coli isolates and total heterotrophic bacteria populations were cultivated from 6 sampling sites up and downstream of WWTPs, and evaluated for resistance to selected ABs. Samples were collected over a 9-month period in the Carter's Creek watershed of College Station, TX. E. coli isolates were tested for resistance to ampicillin, tetracycline, sulfamethoxazole, ciprofloxacin, cephalothin, cefoperazone, gentamycin, and imipenem using the Kirby-Bauer disc diffusion method. HPCs were cultivated on R2A amended with ampicillin, ciprofloxacin, tetracycline, and sulfamethoxazole. Significant associations (p < 0.05) were observed between the locations of sampling sites relative to WWTP discharge points and the rate of E. coli isolate resistance to tetracycline, ampicillin, cefoperazone, ciprofloxacin, and sulfamethoxazole; and an increased rate of isolate multi-drug resistance. The abundance of AB-resistant HPCs was significantly greater (p < 0.05) downstream of WWTPs for all treatments; however, there was no spatially significant difference when normalized to total HPCs cultivated with no AB. Results suggest that the effects of human development, specifically the discharge of treated WWTP effluent into surface waters, are potentially significant contributors to the spread and persistence of AB resistance in the surrounding watershed.